Conventional spray painting systems utilize relatively high pressure air (usually greater than 10 psi) to atomize paint in a spray gun. The atomized paint is transported to the surface to be painted however only a fraction of the paint is actually deposited. The transfer efficiency of atomized paint and volatile thinners actually deposited on the surface to be painted is of the order of 30-40%. The remaining relatively large amount of volatile chemical and paint is released to the atmosphere and is usually called over spray. Increased over spray reduces painting efficiency and increases paint costs and environmentally unfriendly discharges.
The State of California has, for instance, imposed strict regulations on spray painting for the purpose of curtailing the uncontrolled release of volatile chemicals into the atmosphere. These regulations require a transfer efficiency of at least 65% and in air spraying systems the use of air pressure less than ten pounds per square inch (psi). As a result a different approach has been taken with respect to the spray paint systems which are used. The so called high volume low pressure (hereinafter HVLP) spray painting systems have come into greater use in order to increase the transfer efficiency and decrease the over spray. The HVLP system utilizes a turbine to supply a high volume of low pressure air to a specially adapted spray gun.
Premature failure of HVLP blower motors due to insufficient cooling continues to be a problem. A blower motor which drives a blower turbine in an HVLP blower requires constant cooling in order to avoid overheating of the motor windings. To achieve the necessary cooling the blower motor has a cooling fan dedicated to continuously flowing cooling air over the motor.
Current HVLP blowers discharge the cooling air randomly back into the atmosphere or direct it into the turbine. The problem with discharging randomly back into the atmosphere is that hot cooling air exhaust is often sucked back into the cool air intake leading to overheating. Alternatively discharging the cooling air exhaust into the turbine is also not effective. When HVLP air is not required of the spray gun, back pressure develops interfering with the flow of cooling air over the blower motor.
The high transfer efficiency rate of the HVLP spraying painting system make them ideally suited for painting in confined spaces. They are being utilized in, for example, painting and refinishing of bathtubs and sinks in domestic and industrial installations. Nevertheless when spray painting in confined areas such as bathrooms proper ventilation and efficient removal of paint over spray continues to be a problem. The over spray releases volatile chemicals and solvents during spray painting and creates an unwanted odour which can easily spread throughout an entire building when painting bathtubs or refinishing sinks.
Accordingly, there is a need for an improved HVLP blower overcoming blower motor cooling problems. There is also a need for a spray painting system which minimizes over spray generation and preferably contains and/or controls the release of over spray fumes, volatile chemicals and solvents to a predetermined area.